Ah jeez, lets see.
I had a vet a vet look at my horse for a couple minutes, and immediately try to convince me that she had cancer, and would be dead in six months. She's still kicking a couple years later!
I had a trainer try to convince me to sell my little POA mare, because she would "never be a good pony". I think she just had no clue what to do with the mare, so she decided to try and convince us to get a made horse instead. We left her, and now I am constantly getting people trying to buy the pony off me.
I was riding a very green pony in a lesson once, and I had the trainer try to convince me to put a tie down on her. I've also been told, by various people, to put a tie down on my then green horse, who had a head tossing issue.
I had the same trainer try to make me raise the bit on a different pony, because it wasn't creating any wrinkles. Even after I informed her that the pony had some issues with pressure, and went best with a lower bit.
We had somebody out to work with our filly a couple years ago, and her 4yr old son tagged along. Somehow, being a teenage girl, I always seem to be the one put in charge of entertaining small children, so he was following me around the barn. I got a little 12hh pony out to work, and we started talking about her. He informed me that she was not a real pony, because she was missing body parts. It took me a minute to figure out what he was talking about, he was referring to her trace clip